The background art of the present invention will be described by taking a shovel as an example. The shovel comprises a lower traveling body, and an upper slewing body mounted on the lower traveling body.
FIG. 5 is a top plan view of the upper slewing body, and FIG. 6 is a back view of a rear end of the upper slewing body.
The upper slewing body comprises an upper frame 1 as a base thereof, and a non-illustrated working attachment attached to one end portion (in FIG. 5, left end portion) of the upper frame 1 (The following description will be made on an assumption that this end a “front” end). The working attachment includes a boom, an arm and a bucket.
The upper slewing body further comprises: three partition walls 2 to 4 each extending in a right-left direction; an engine 6; a combination of a cooling fan 7 and a heat exchanger 8 as cooling equipment; a hydraulic pump 9; and an exhaust gas aftertreatment device 10.
The partition walls 2 to 4 define an engine compartment 5 on a rear region of the upper frame 1. Within the engine compartment 5, the engine 6 is provided, and the cooling fan 7 and the heat exchanger 8 such as a radiator are installed on a left side of the engine 6.
The hydraulic pump 9 is provided on a right side of the engine 6 while being connected to an output shaft of the engine, and the exhaust gas aftertreatment device (additionally serving as a muffler) 10 is installed on the right side of the engine 6 in a posture where it extends transversely across an upper side of the hydraulic pump 9.
The exhaust gas aftertreatment device 10 comprises: an exhaust gas purifying device 14 comprised of a DPF (Diesel Particulate Filter) for removing PM (Particulate Matter) such as soot contained in exhaust gas and provided in an engine exhaust passage; and a NOx reducing device 15 comprised of an SCR (Selective Catalytic Reduction) system for decreasing NOx emissions and provided in the engine exhaust passage at a position downstream of the exhaust gas purifying device 14, as disclosed, for example, in JP 2013-224542 A.
The NOx reducing device 15 comprises a device body (reference sign is omitted) for performing a urea-based selective catalytic reduction (SCR) reaction for NOx, and a tail pipe (exhaust stack) 16 for releasing treated exhaust gas from the device body to the outside. In some cases, the device body of the NOx reducing device 15 is disposed in side-by-side relation to the exhaust gas purifying device 14 in the right-left direction.
The NOx reducing device 15 further comprises a mount table 13. As illustrated in FIGS. 5 and 6, the mount table 13 has a top pate 11, and a plurality of support legs 12 and the mount table 13 is arranged to stride over the hydraulic pump 9 so as to support the exhaust gas purifying device 14 and the device body of the NOx reducing device 15. The exhaust gas purifying device 14 and the device body of the NOx reducing device 15 are installed on the top plate 11 of the mount table 13 (also, see JP 2013-224542 A).
The NOx reducing device 15 further comprises: a NOx sensor configured to detect an amount of NOx contained in exhaust gas; a urea solution injection control section (Dosing Control Unit: DCU) configured to control an injection amount of urea solution; and a NOx controller configured to send, as NOx information, a signal from the NOx sensor to the urea solution injection control section (none of these components is illustrated).
With a view to shortening a length of a harness to be connected to the NOx sensor, to thereby decrease noise and costs, the NOx controller is installed at a position around the NOx reducing device 15 and close to the NOx sensor.
However, the NOx reducing device 15, particularly, the tail pipe 16, is heated up to extremely high temperatures during engine operation, thereby causing a problem that the NOx controller undergoes heat damage including shortening of usable life, failure, malfunction, and the like caused by the high temperatures.
Moreover, the NOx controller is less resistant to water, and is likely to be adversely influenced by rainwater or washing water intruding into the engine compartment 5.
As a countermeasure against the above problems, it is conceivable to surround the NOx controller by a heat insulating material or a cover with a heat insulating material. However, this countermeasure is inadvisable because it leads to an increase in cost of a construction machine and deterioration in assembleability (installability) of the NOx controller.
It is also conceivable to install the NOx controller at a position away from the tail pipe 16 radiating heat at a level of the highest temperature, as far as possible. However, this countermeasure is less effective, because flexibility in positional selectivity of the NOx controller becomes low due to restrictions on harness length and limitations on space, and a remaining portion of the NOx reducing device 15 other than the tail pipe is also deemed as a high-temperature portion through which exhaust gas flows.